The use of cellulosic fillers in thermoplastics has occurred for at least three decades particularly in the automobile industry. The car industry has utilized wood plastic composites including polypropylene resins melt compounded with woodflour. These wood-plastic composites as they are known today are extruded sheets for indoor parts of some vehicles.
Nonetheless, only a few inroads have been made in using wood-plastic composites in other markets. There are some records about the use of biofibers and cellulosic composites in pencil manufacturing, stationary, fencing and crossties since these areas are seeing the advantages of wood-plastic composites in comparison to conventional wood, such as dimensional stability, lower moisture absorption, fungii resistance and weathering resistance. The woodplastic and vegetal fiber composites can also be entirely recyclable and can be manufactured by means of traditional thermoplastics processing routes as extrusion, injection molding, calendering and so forth. Such characteristics are making the wood composites particularly attractive in many applications for the building industry, injection molded car parts, household appliances and mostly extruded profiles for widespread devices including furniture.
Wood-polymer composites are thermoplastic as compared to products made from lumber alone, and advantageously processed into various shapes. A wood-polymer composite, when seen as a thermoplastic resin, is advantageous in that it affords woody texture, such as appearance (e.g., color tone, gloss etc.), a touch (e.g., thermal conduction, surface roughness) and the like, which are characteristic of lumber, decreases coefficient of thermal expansion, is light weight as compared to inorganic filler products, and so on. Moreover, end lumber pieces, scrap wood, sawdust and the like, which are produced in the lumbering industry, can be used as the wood flour for wood-polymer composites, thereby enabling effective utilization of non-used resources.
However, one of the main problems faced by wood-plastic composites processors is the hygroscopic nature of the wood and, in particular, the relatively low degradation temperature of the cellulose. Thermooxidative degradation of cellulose starts at around 200° C., which severely limits its use in engineering plastics as a substitute for glass fibers. Further, for outdoor applications, fading and yellowness of the composite may occur under ultraviolet (UV) and weathering exposure.
Therefore there is a need for wood-plastic compositions that has improved thermal characteristics and/or improved weatherability.